1. Field of the Invention
The present invention relates to optical disc apparatuses that record and play back optical signals onto and from optical recording media, optical pickups used in optical disc apparatuses, and light detectors provided in optical pickups.
2. Description of the Related Art
Optical pickups that record and play back information onto and from optical recording media capable of recording and playback, such as compact disc-recordables (CD-Rs), digital versatile disc ± recordables (DVD±Rs), or digital versatile disc random-access memories (DVD-RAMs), are available.
Such optical pickups perform recording by irradiating an optical recording medium with a light beam from a light source through an objective lens. In order to monitor output power of a light source when recording is being performed, a light detector formed by integrating a light-receiving device that receives a light beam emitted from the light source and a power monitor circuit section that amplifies a detection signal output from the light-receiving device and that generates a power monitor signal on the same semiconductor substrate (semiconductor chip) is proposed (see, for example, Japanese Unexamined Patent Application Publication No. 2003-257070).
In the light detector, the power monitor circuit section includes a current-voltage conversion circuit that converts a detection signal, which is a current signal output from the light-receiving device, into a voltage signal and an amplifying circuit that amplifies the voltage signal.
In addition, in order to adjust the level of a power monitor signal, a variable resistor (volume) for changing the gain of the amplifying circuit is externally disposed with respect to the semiconductor substrate. The variable resistor is mounted on a substrate different from the semiconductor substrate.